Wall street made an interesting discovery last week. Apple, the iPod and mobile phone company, also makes computers! Shock! Horror! This elementary fact had hitherto escaped the notice of investment analysts, hypnotised as they were by the glamour of the iPod, the implosion of the music industry and the belief - ably fostered by Dell & Co - that making computers was a low-end, commoditised business.

What prompted the discovery was the release of Apple's latest results, which showed soaring revenue, sales and net profit. For the quarter ending 31 March, the company reported revenues of $4.36bn and a net profit of $410m. The comparable figures for the same quarter last year were $3.24bn and $290m respectively. Yet the market rewarded Apple's sterling performance by marking down its shares by 3.4 per cent (though they finished the day up by 1.7 per cent, at $162.89).

Perhaps the initial decline was triggered by the discovery that much of Apple's buoyancy was provided not by iPods or iPhones, but by boring old computers. Well, boring new computers, actually. It turns out that Apple sold 2.29 million laptops and desktops during the quarter, which represents a 51 per cent rise on the same quarter last year. And this is just a continuation of an older story.

The market research firm IDC calculates that in 2007 Apple sold 7.8 million desktop and notebook computers, capturing 3 per cent of the global market. The same source reports that Apple sold 4.2 million computers in the US, which amounted to 6 per cent of the market. That was up 34 per cent on 2006 and five times the industry average.

So how come Wall Street was so surprised about all of this? In a phrase: iPod mania. 'What always gets lost - because everything is focused on iPhones, iPods, iPills, whatever - is Mac sales,' said Scott Rothbort, a veteran investor in Apple. 'Mac sales, Mac sales, Mac sales - that is the story of this company. The Macintosh is capturing more and more market share.'

Apple is always going to be a minority player, but 6 per cent of a colossal market makes for a very nice niche. The best way of looking at it is to say that Apple is the BMW of the computer industry: minuscule in comparison with Toyota, GM and Ford, but a driving force nevertheless because of design, functionality and fanatical customer loyalty. It sets the standards that the others eventually have to reach.

The most intriguing hypothesis is that the surge in Mac sales is connected with the ongoing difficulties associated with Vista, the latest incarnation of Microsoft's Windows. Although Microsoft continues to insist that the Vista rollout is going just fine, the word on the street - or at any rate the streets patrolled by this columnist - says otherwise. I've lost count of the number of people who have rolled their eyes to heaven when quizzed about how they're getting on with the new system.

The problems appear to be clustered in two main areas - inadequate or missing software 'driver' programs for peripherals like printers and modems; and the fact that old, tried-and-tested applications simply won't run any more. Small wonder that people are 'upgrading to XP' - in fact, downgrading from Vista to the older version of Windows. 'At least,' said one downgrader who sought my advice, 'it's the devil I know.'

All of which explains why the date on which Microsoft will cease to support XP has become such a hot topic. Initially, support for the XP Home edition (the one most ordinary customers use) was quietly extended to 'two years after the next version of this product is released' - or two years after the release of Vista. But this has failed to quell user unrest - which may explain why Microsoft chief executive Steve Ballmer dropped some hints in Belgium last week. 'XP will hit an end-of-life. We have announced one,' he said enigmatically. 'If customer feedback varies we can always wake up smarter, but right now we have a plan for end-of-life for new XP shipments.'

Lest anyone accuse me of bias, I should say that Leopard, the latest version of the Mac operating system, has suffered similar problems. Lots of venerable Adobe software (PhotoShop CS, for example) simply won't run on it. When I logged on to the Adobe website seeking help I was told that anyone trying to run CS was 'likely to encounter issues for which there is no resolution'.